/Engine/Source/Editor/UnrealEd/Public/ThumbnailHelpers.h
class FParticleSystemThumbnailScene : public [FThumbnailPreviewScene](API\Editor\UnrealEd\FThumbnailPreviewScene)
UParticleSystem...
PartComponent
The particle system component used to display all particle system thumbnails
FFXSystemInterf...
ThumbnailFXSystem
The FXSystem used to render all thumbnail particle systems